The basic hypothesis of this proposal is that the ability of alpha 1 and alpha 2 adrenoceptor agonists to stimulate the Na+/K+ pump of vascular smooth muscle is related to the activation of a Na+ influx pathway(s). The activation of Na+ influx via the two alpha adrenergic receptor subtypes is very likely mediated by different signal transduction mechanisms. The proposal will be aimed at investigating this hypothesis in quiescent and proliferating vascular smooth muscle cell culture. The culture systems may serve as a model of normal, differentiated vascular cells (quiescent) or as a model of certain diseases states in which cells are proliferating such as atherosclerosis or hypertension. Cells maintained under quiescent or proliferating conditions will be characterized with respect to Na+/K+ pump number by (3H) ouabain binding, turnover rate of the Na+/K+ pump by monitoring ouabain-sensitive 86Rb uptake, 22Na influx and numbers of alpha 1 and alpha 2 receptors by (3H) prazosin and (3H) yohimbine binding. To establish the mechanism of Na+ influx in activation of the Na+/K+ pump, pharmacological antagonists of Na+ transport will be used; amiloride and its analogs to differentiate between Na+/Ca++ exchange and Na+/H+ exchange and the loop directors, furosemide and bumetamide, to identify Na+/K+/Cl- co transport. A central effect of alpha 1 and alpha 2 adrenoceptor occupation in vascular smooth muscle is a rise in (Ca++)i. Studies will be performed to determine the role, if any, of alpha adrenoceptor- mediated Ca++ elevation in Na+/K+ pump stimulation. This will be accomplished by artificially manipulating (Ca++)i and observing the effects on Na+/K+ pump function. Activation of Na+ influx is known to be an early signal for proliferation in many cell types. Therefore, it is also planned to assess the effect of long-term exposure of possible mitogenic effects of alpha adrenoceptor of cell proliferation. In these studies, it is expected that significant data will be obtained regarding the control of active and passive ion movements in vascular smooth muscle. In view of the role that disturbances of ionic regulation are believed to play in hypertension, it is anticipated that these studies may contribute to the understanding of this disease process.